Strange Tang Discoloration

[c_kyle]

I'm working on an Imperial, and have come across something strange.

Before (It's the middle razor)



Current State:




You can't really tell from the before pic, but there was bad pitting and corrosion on the tang. The strange part is the discoloration starting before the pivot hole. The sides of the razor have been wet-sanded with 500 grit paper so far. The finer I get with the sanding, the more pronounced the discoloration becomes.

Anyone have any idea what this might be? The sides of the blade and all of the tang are perfectly flat, so it's not an angle change that's causing an optical illusion. On the other side of the tang, the discoloration is exactly the same.